1. Field of the Application
The present invention relates to furnaces for vacuum arc melting of highly reactive metals such as titanium and zirconium, and can be used for melting refractory metals such as tungsten and molybdenum.
2. Description of the Prior Art
There is known in the art a furnace for vacuum arc melting of titanium and titanium-based alloys, which comprises a vacuum chamber fitted with a cover having fixed therein an electrode holder spaced above a cooled mould whose bottom is sealed with a detachable bottom plate. The cooling spaces of the mould, bottom plate and that of the electrode holder are filled with a liquid-metal cooling agent (eutectic NaK alloy).
The coolant used in the vacuum chamber is water which circulates in the first cooling circuit. The cooling space of the mould and that of the bottom plate intercommunicate with each other and with an expansion chamber, communicating as well through pipes with a separately arranged air,- or water heat exchanger which comprise the second cooling circuit. The cooling chamber of the electrode holder is brought in communication also by means of pipes with another heat exchanger comprising the third circulation circuit.
In the event of thermal expansion of a liquid-metal coolant the furnace is provided with two expansion vessels filled with a neutral gas such as argon. In addition, the circuit which comprises the mould and bottom plate is provided with a means for cleaning the liquid-metal coolant from oxides.
However, throw-out of liquid alkali metal from the circuit exterior section may possibly to occur during operation due to corrosion-and-erosion attack on the pipeline, caused by the flowing liquid-metal coolant. This type of destruction is very difficult either to predict or control.
Moreover, in case of failure in the eutectic alloy cleaning operation, the pipeline of the cooling circuit system incorporating the water-cooled mould and bottom plate may be blocked by the coolant solid oxides, which may disrupt the furnace operation. In addition, the destruction of pipes in the air-, or water heat exchanger may become the cause of explosion or fire.
The present invention provides an apparatus for vacuum arc skull melting of titanium or its alloys, wherein the exterior section of the liquid-metal circuit is nonexistent.
This apparatus is constructed so that a cooling agent (eutectic NaK alloy) is found only in the cooling space of a crucible, in communication with an expansion chamber. Mounted in said chamber filled with a cooling agent is a water-cooled heat exchanger adapted to produce a signal on leakage of water or eutectic NaK alloy in the event of defect in the heat exchanger pipes.
However, the attempt to eliminate the possibility of contact between water and eutectic NaK alloy by means of special construction elements or else by way of continuous control over the heat exchanger leak-proof sealing in the process of melting results in more complicated furnace construction and fails to provide the furnace operating reliability.